The invention relates generally to continuous casting.
More particularly, the invention relates to a method of and an apparatus for oscillating the mold in a continuous casting installation, especially an installation for the continuous casting of steel.
During continuous casting, and particularly the continuous casting of steel, the continuous casting mold is oscillated in order to introduce lubricant between the mold wall and the shell of the continuously cast strand. The purpose is to prevent or reduce sticking of the shell to the mold wall.
Various oscillation mechanisms and methods have been proposed for the continuous casting of steel. Mechanical oscillation drives which generate a sinusoidal motion are in widespread use. The sinusoidal oscillatory motion has proven to be satisfactory at low and medium casting speeds, i.e., strand speeds.
From the West German Auslegeschrift No. 2 002 366 it is known to adjust the sinusoidal oscillatory motion for high casting speeds by increasing the stroke in proportion to the strand withdrawal speed. In other publications, it is also proposed to increase the frequency in dependence upon the strand withdrawal speed. If the characteristics of the relative motion between a moving strand shell and a sinusoidally oscillating mold are proportionally carried over to high strand withdrawal speeds, e.g., speeds between 2 and 6 meters per minute, a correspondingly large stroke or high frequency, or an increase in both stroke and frequency, must be achieved. Satisfactory results cannot be obtained with this type of oscillation, particularly for steel grades such as the so-called sticking grades which are difficult to cast.
Oscillatory motions other than the sinusoidal oscillatory motion are also known, for example, from the Japanese published specification No. 61-162 256. As a rule, the time periods for the upward and downward strokes in these non-sinusoidal oscillatory motions are unequal, e.g., the time periods are in a ratio of 1:3. On a plot of displacement versus time, such oscillations are represented by a sawtooth-shaped line. The mold can be driven by an hydraulic or equivalent drive unit. Oscillation drives which generate a non-sinusoidal motion are easy to regulate as regards stroke and frequency. Nevertheless, the quality of the strand surface, particularly for steel grades designated as sticking grades, is unsatisfactory because of oscillation marks and the occurrence of breakouts in the mold at high casting speeds.